Recent data indicates that EP1 is a cholesterol exchange protein and that it is synthesized and secreted by all epithelia. Therefore, we have concentrated our efforts on determining the role of EP2 in the fertilization process. We have shown that EP2 is an androgen-dependent, epididymis-specific secretory protein that is synthesized and secreted specifically in the caput region of the chimpanzee epididymis. We have identified several other alternative EP2 messages, which we have not yet characterized. Further, the alternative splicing pattern for chimpanzee is different from that of the rhesus monkey. The rhesus monkey uses several additional exons to transcribe the three open reading frames. To better understand the splicing variants and their two promoters, we began work on a genomic EP2 clone (PAK). PAK (P1 artificial chromosome), has an insert size of over 100 kb that appears to contain the entire EP2 gene. Preliminary analyses, using PCR to bridge the intr ons, indi cates that the EP2 gene contains at least 10 exons, five of which are used in the EP2A variant and the last 3 of which are used in the EP2B variant. We have shown that EP1 does not bind to the sperm surface. Western blots of proteins from ejaculated chimpanzee sperm showed intensely stained components only in low salt extract. Using immunohistochemical staining, we showed that EP1 appears to be synthesized and secreted primarily by epithelia VI-VIII of the mid-caput through epithelium IX of the distal caput-proximal corpus transition of the ductus epididymides of the chimpanzee. FUNDING NIH / RR0599407 $165,627 4/15/97 - 8/14/01 PUBLICATIONS *Smithwick, E.G., Gould, K.G. and Young, L.G. Immunohistochemical localization of epididymal secretory protein EP1 in the adult male chimpanzee (Pan troglodytes). Tissue and Cell (In press). *Young, L.G., Frolich, O. and Gould, K.G. HE2/EP2, an androgen dependent protein of the chimpanzee (Pan troglodytes) epididymis. J. Reprod. Fert. (In press). P51RR00165-38 1/1/98 - 12/31/98 Yerkes Regional Primate Research Center